Process for drying sheet material with air



Jan. 20, 1959 Filed April 25, 1956 W. BUSCHMANN ETAL PROCESS FOR DRYING SHEET MATERIAL WITH AIR 2 Sheets-Sheet 1 I 0 I /'x (CELLULOSE FILM) I l I 1 I l l I WEIGHT GRAM av mann v OF CELLULOSE. FILM FIG. 2

l l l l 7 so 55 so 55 10 1s SPEED or CELLULOSE FILM METERS/MINUTE JNVENTORS: WALTER BUSCHMANN WALTER BUHREN ATT YS Jan. 20, 1959 Filed April 25, 1956 w. BUSCHMANN ETA L 2,869,246

PROCESS FOR DRYING SHEET MATERIAL WITH AIR 2 Sheets-Sheet 2 INVENTORS: WALTER BU'SCHMANN WALTER Bl'JHREN ATT'YS United States Patent PROCESS FOR DRYING SHEET MATERIAL WITH AIR Walter Buschmann and Walter Biihren, Wuppertal- Barmen, Germany, assignors to J. P. Beinherg Aktiengesellschaft, Wuppertal-Oberbarmen, Germany Application April 25, 1956, Serial No. 580,638

Claims priority, application Germany April 26, 1955 3 Claims. (CI. 34-23) current of heated air against the material as it passes around a plurality of cylindrical drums or rollers. Drying can be accomplished exclusively by the heated air which is preferably recirculated, or the cylindrical rollers ordrums can also be internally heated by the introduction 'of steam for an additional drying effect. Air is directed against the material on the drum by a plurality of slotshaped vents associated with each cylinder and disposed transversely with respect to the path of the material. The jet of heated air from the vent is preferably directed in such a manner that the flow of air is approximately perpendicular to the material. The openings in the vents through which air is blown have the same or a greater transverse width than the material being dried.

It has now been found that materials ordinarily dried by this conventional process-are damaged by excessive drying of the edge zones or areas of the material. Also, the properties of the finished product have been found to be unfavorably affected by this excessive drying, particularly in the case of a cellulose film.

One object of the invention is to provide an improved process and apparatus for air drying of an elongated, thin, flexible material of substantial width such as films, foils, ribbons, Woven fabrics and the like.

Another object of the invention is to provide an improved process and apparatus for air drying whereby excessive damage caused by unequal drying effects can be avoided, particularly the excessive drying of the edges of an elongated, thin, flexible material such as a cellulose film.

Still another object of the invention is to provide an improved process andapparatus for air drying which will reduce, the amount of spoiled material caused by improper drying and thus reduce costs.

Yet another object-of the invention is to provide an improved process and apparatus for air drying which can be easily adapted to a conventional cylinder dryer of the .typeherein described.

These and other objects and advantages of the inven- ,tion will be more clearly understood upon a consideration tion of a cylinder dryer constructed in accordance with the invention and illustrating a plurality of vents through which air is directed'or blown onto material passing around a cylindrical roller;

Fig. 4 is a perspective view of the same with parts omitted, illustrating the construction of a single vent of the type shown in Fig. 3; and

Fig. 5 is an enlarged cross-sectional view taken on'line 5--5 of Fig. 4.

In accordance with the invention, an improved process for air drying is provided'wherein heated air in an intermediate portion of the drying process is directed onto a central area of the material through openings in the slotshaped vents which are so arranged as to blow air on an area increasing constantly from the beginning of the intermediate portion to the end thereof within a limit of about 50% to of the width of material. The intermediate portion of the drying process preferably corresponds to about the middle one-third of the drying apparatus, i. e. the middle one-third of the total length of material in engagement with the cylindrical rollers for drying.

The central area onto which air is blown at the beginning of the intermediate portion of the drying process is preferably maintained at a constant value within a limit of about 50% to 70% of the width of material. Thereafter, the width of this area continuously increases to the end of the intermediate portion where the central area is about 90% of the width of material. In those portions of the drying process or apparatus preceding and following the intermediate portion, heated air is blown across the full width of the material being dried. Other drying conditions are advantageously determined such that the surface water or moisture content of the material is removed in the first or preceding portion of the process or apparatus. It is advantageous to have removed substantially all surface moisture content at a point just before the material enters the intermediate portion.

A conventional cylinder drying apparatus is conveniently modified for application of the improved process by combining therewith successive slot-shaped vents positioned in an intermediate portion, preferably about the middle one-third, of the drying apparatus and adapted to direct heated air through the opening of each of the vents onto a central area of material being dried. These successive slot-shaped vents are so constructed and arranged as to constantly increase the transverse width of the openings therein from the beginning of the intermediate portion to the end thereof. Means are preferably provided for adjusting the width of the opening in each of these vents, for example, by a pair of sliding covers adapted to slide back and forth across each opening.

Referring now to the drawings, Fig. 1 and Fig. 2

illustrate two procedures which can be followed to obtain a satisfactory drying efiect when materials of diiferent thickness or different weight are to be dried.

In Fig. 1, the material being dried is schematically represented by the rectangular area and corresponds to the intermediate portion or middle one-third of the drying process in which the intermediate portion begins at the base line a and ends at the top line b while the side lines 0 and 0 represent the edges of the material. The arrow indicates the direction in which the material travels as it is dried. The dotted lines d and d enclose a central area onto which heated air is directed by a plurality of successive slot-shaped vents with openings in which the transverse width of the openings continuously increases from 50% of the width of material at a to 90% of the width of material at b. Similarly, the dotted lines e and e enclose a central area which increases from 70% to 90% of the width of material. At a constant rate of speed of material passing through the drying process, the degree of drying can be regulated to accommodate a diffe'rent thickness of material by adjusting the opening in the first vent (a) to a desired value between 50% and 70% of the width of material, and then adjusting successive openings to produce a continuously increasing width to about 90% of the width of material at the last vent (b). v

In drying for example a cellulose film the width of the opening of the first vent is most advantageously determined as a linear function of the weight of the film per square meter such that this width is increased linearly from about 50% to 70% as the weight of the film increases from about grams per square meter to 45 grams per square meter based on the dry weight of the film.

The degree of drying can also be regulated to accommodate materials of different thickness by adjusting the rate of speed at which the material passes through the drying process. For a constant width of the central farea of material being dried in the intermediate portion of thedrying process, the required change in this rate of speed is linear with respect to the change in weight of 'materi'al per square meter within the range of ordinary operations.

In drying a cellulose film according to the invention as described before, the graph in Fig. 2 illustrates that where the width of the central area upon which air is blown at the beginning of the intermediate portion is 'maintained constant at about 50%, the rate of speed of the film passing through the drying process is decreased linearly from about 75 meters per minute to 52 meters per minute with respect to an increasing weight of the film from about 25 grams per square meter to 45 grams per square meter based on the dry weight of the film.

One embodiment of the improved portions in combination with a cylinder drying apparatus is illustrated in Figs. 3, 4 and 5. Fig. 3 shows a cellulose film material 1 as it passes around one cylinder roller 2 in an intermediate portion of a cylinder dryer having a plurality of cylindrical rollers as indicated by 3 and 4. A plurality of slotshaped vents 5 are positioned successively in the vicinity of the cylindrical roller 2 so that the opening 6 of each vent is disposed transversely 'with respect to the path of the film material 1 as it passes in a longitudinal direction around the roller 2 as indicated by the arrow. A manifold 7 connects the individual vents for substantially equal distribution of heated recirculated air introduced at inlet 7a, the air being blown through the openings of the vents in a direction of flow approximately perpendicular to the material being dried.

Each vent 5 in this intermediate portion of the cylinder dryer is constructed so as to direct air only upon a central area of the film material 1 by providing a pair of adjustable, sheet metal, slide covers 8 ands which can be moved back and forth on either side of the opening 6 as shown more clearly in Figs. 4 and 5. The slide covers -8-and 8' have oppositely disposed transverse lips 9 which are inwardly 'rounded'to slidingly engage in outwardly and oppositely r ounded'lips 19 forming the transverse edges of the opening 6. Nuts 11 and 11 are rigidly connected to each cover 8 and 8"an'd threaded on the rod 12 which is provided with a right hand thread on one'side and a left hand thread on the other side of the opening. The threaded rod 12 is rotatably supported in the lateral bearings 13-and 13 and extends outwardlyfrom one sideof 4 the vent 5 to receive a crank or handle 14 bywhich the rod ill-can be rotated. Rotation of the crank 14in one direction thus closes the slide covers 8 and 8' over the opening 6 while rotation in the opposite direction exposes a greater width of opening. The opening 6 inthe vent 5 is preferably permanently closed at its oppositely disposed transverse sides by sealing members 15 and 15' so that no air will escape at the sides when the slide covers 8 and 8' are urged inwardly to cover the opening.

The improved apparatus as described hereinabove thus provides an intermediate portion of a cylinder drying apparatus in which the size of openings can be expanded or reduced as desired to accommodate various thicknesses and weights of materials during continuous operation. These improvements can be readily adapted to a conventional cylinder drying apparatus and provide improved drying results with theadditional advantage of flexibility in operation.

The invention is hereby claimed as follows:

1. In a process 'for drying an elongated, thin, flexible cellulose film of substantial width in which a cellulose film is passed longitudinally in a path around a plurality of cylindrical rollers and dried by directing heated air upon said film, said heated air being blown through a plurality of slot-shaped vents successively positioned adjacent each of said rollers and disposed transversely with respect to the path of said film, the improvement which comprises: directing heated air in a first portion of said drying process through successive vents onto the entire width of said cellulose film until substantially all'surface water content of said film has been removed; thereafter directing the heated air in an intermediate portion of said drying process through successive vents onto a central area increasing constantly from within a limit of about 50% to of the width of said film at the beginning of said intermediate portion to about 90% of the width of said film at the end of said intermediate portion, and after said intermediate portion again directing heated air over the entire width of said cellulose film.

2. An improved process as defined in claim lwherein at a constant rate of speed of said cellulose film passing through the drying process, the width of the central area of said film upon which air is blown at the beginning of the intermediate portion is increased linearly from about 50% to 70% of the film width with respect to an increasing weight of cellulose film of from about 25 grams'per square meter to 45 grams per square meter based on the portion is'maintained constant at about 50% of the film width and the rate of speed of said film passing through the drying process is decreased linearly from about meters perminute to 52 meters per minute with respect to an increasing weight of film material of from'ab'out 25 fi'grams'pe'r square meter'to 45 -gramsper square meter.

References Cited in the file of this patent UNITED STATES PATENTS 1,298,655 Briner Apr. 1, 1919 2,330,395 Sullivan Sept.'28, 1943 2,349,558 Otfen May 23, 1944 

